DESCRIPTION: (Applicant's Abstract) The proposed study builds on a NORC preliminary study by integrating epidemiology and ethnography under a social network approach to study HIV risk behaviors among injection drug users (IDUs) and their sexual and injection partners in Washington, DC. Relatively little research on IDUs is being conducted in Washington, even though, among U.S. states and territories, it has the highest AIDS rate in the country. The prospective study of 200 index IDUs and about 600 of their sexual and injection partners (conjugates) has several aims including describing and analyzing individual and network characteristics of IDUs and their partners, including changes over time; examining differences among groups of IDUs in terms of risk behaviors and their correlates; studying HIV risk behaviors at multiple levels of individual-, network-, and neighborhood-level effects; and testing a theory of network access to resources to determine its validity as an explanation of IDU risk behaviors. A two-stage targeted snowball sampling procedure is used to recruit 200 index subjects allocated to 12 cells (2x2x3) representing a cross-tabulation of gender, age (split at age 30), and race/ethnicity; and approximately 600 of their injection and sexual partners. Three diverse neighborhoods provide the initial recruitment locations. Index and conjugate subjects participate in four, periodic (six month intervals) epidemiological interviews designed to gather extensive data on sociodemographics, detailed sexual and drug use behavior, and social networks. They also supply a blood sample for HIV testing. Additional data are aggregated to the network level from these individual-level data. Moreover, data are supplemented by extensive ethnographic information (e.g., participant observation, in-depth interviews) designed to more fully understand the context, patterns, and norms of IDUs and their social networks; and by Census and other official data sources to better assess socioeconomic processes at the macro level. Data analysis with UCINET, log linear modeling, and multilevel modeling is designed to measure, describe, and compare characteristics across networks and over time; and assess how these affect HIV risk behaviors. In brief, the research extends previous studies of IDUs by (1) interviewing index subjects as well as conjugate subjects; (2) following the same index and conjugate subjects and their networks over four waves of data collection; (3) modeling simultaneously HIV risks due to sexual activities and injection drug use; and (4) encompassing multiple levels of explanatory variables affecting HIV risks, including individual-, network-, and neighborhood-level explanatory variables.